Many people with binocular vision disorders never have these binocular disorders improved to the fullest extent. Corrective lenses establish normal visual acuity for many people, but the underlying visual disorder persists. Lenses alone cannot compensate for some disorders.
If vision is poor or hampered in one or both eyes, fusion (the brain's ability to use both eyes together and thereby attain and maintain depth perception) cannot occur and ocular alignment is lost due to a partial loss of brain control.
Presently, treatment of binocular disorders such as decompensated phoria, strabismus, suppression, amblyopia and accommodative insufficiency, explained below, is accomplished through widely varying techniques. However, all these techniques may be improved, or at least alternative solutions are desirable in some cases.
A strabismus can be manifest or latent. A manifest strabismus is commonly just called a squint, strabismus or tropia and the visual axis are not directed towards a common object (as illustrated in FIG. 2). A latent strabismus is commonly called a heterophoria or just phoria. This is a deviation of the visual axis in which is only apparent when one eye is covered.
Most people have a phoria without the phoria causing inconvenience in their everyday life. However, if a person having a phoria is exposed to deviating situations, such as when the person is put under stress, becomes sick, or the demand on the visual system increases by other reasons, the vergence system might not overcome the phoria. Such reasons may comprise extended work with display devices, work in badly illuminated environments, etc. A decompensated phoria is then established, wherein a decompensated phoria can be classified as one or more of a) Convergence insufficiency—the person is not able to overcome the phoria in near vision by means of convergence and the baseline phoria is outwards; b) Convergence excess—the person is not able to overcome the phoria in near vision by means of divergence and the baseline phoria is inwards; c) Divergence excess—the subject is not able to overcome the phoria in distance vision by means of convergence and the phoria is outwards; d) Divergence insufficiency—the subject is not able to overcome the phoria in distance vision by means of divergence and the phoria is inwards.
If a decompensated phoria is left untreated, strabismus and suppression will start to develop, wherein suppression is a mechanism in which the brain suppresses the image from one eye to avoid diplopia, i.e., double vision. Visual capability thus established by the eye that is not suppressed may again be fully sufficient without causing a major inconvenience in these persons everyday life good, in particular if the suppressed eye is occluded, e.g. by means of an eye patch. However, if left untreated, the suppression may develop further to an amblyopia. An amblyopia is vision disorder of degraded visual capability which is present even though a suppressed eye is occluded. If amblyopia and/or strabismus is left untreated it may degrade into abnormal retinal correspondence. Abnormal retinal correspondence (ARC) is a means by the brain to establish an alternative binocular vision in which the fovea of the good eye starts to correspond with a point outside the fovea of the other eye. Normally this point is equally distanced from the fovea as the angle of the squint.
The field of vision training involves therapy to improve the aforementioned visual disorder conditions, such as decompensated phorias, strabismus, suppression and amblyopia. For providing such therapy, an eye specialist, such as an orthoptist, optometrist or ophthalmologist, may prescribe visual tasks to be practiced under controlled conditions. The treatment of strabismus is for instance aimed at: a) eliminating an existing amblyopia, and b) realigning the eyes to restore binocular perception. A treatment of decompensated phorias is provided to eliminate an eventual suppression and to increase the vergence reserves. In accommodative insufficiency the aim is to increase the accommodative ability.
In DE 10207839 an apparatus for biofeedback for strabismus treatment is disclosed. The disclosed apparatus makes use of two unique images, one for each eye. For the eye which visual axis is miss-aligned, the corresponding image is spatially moved in such a way that the alignment of the image is no longer mis-aligned with respect to the visual axis of the eye. However, the image will be detected at a different area of the retina of the miss-aligned eye and as the visual cortex is used to connect areas from both eyes to interpret the visual information. The miss-aligned eye to which such compensated images are presented then tries to redirect itself to achieve the desired mis-aligned position as before, where corresponding visual information is used to be detected to gain “normal” vision for the person. This means that the eye will try to compensate even more than under “normal” strabismus vision. Hence, the apparatus of DE 10207839 is not suited to provide a suitable therapy, such as perceptual motor learning.
In U.S. Pat. No. 4,756,305 a similar eye training device is disclosed that alters refractory viewing by adding a refractive element such as a prism. Then strength of prisms is gradually reduced over a long-term treatment. However, the strength of the prisms is only adjusted by a doctor. Between visits of the patient to the doctor, the prisms are locked in place. Further, the device of U.S. Pat. No. 4,756,305 is not suited to provide vision therapy where amblyopia is eliminated, and only tries to realign the eyes to restore binocular perception. As therapy is only adjustable by the doctor and times between visits may be long, this device is not well suited for the therapeutic purpose.
In US 2001/0050754 a method for treating amblyopia in children is disclosed. A pair of eyeglasses or goggles is provided with an electrically and selectively darkenable lens, such as am LCD lens, so that for selected portions of time, one or the other eye may be occluded. In one embodiment, circuitry for providing pulses of a selected width to one or both lenses is incorporated in the eyeglasses or goggles, with the lens associated with the deviating eye receiving a wider pulse than the lens associated with the other eye. Thus, the deviating eye is occluded for a longer period of time than the normal eye. In another embodiment, a computer is coupled to the eyeglasses or goggles, and is provided with a program of interest to the child which selectively occludes the deviating eye.
The application US 2001/0050754 discloses an advanced version of an eye-patch and is not suitable to provide binocular therapy, such as perceptual motor learning, as explained above.
In US 2003/0214630 an interactive occlusion system is disclosed, including software and hardware, for the treatment of amblyopia using virtual reality or other physically interactive or perceptually immersive three-dimensional or two-dimensional computer generated simulations, in which the patient's occlusion compliance and usage time during occlusive and non-occlusive periods can be precisely recorded and the patient's visual acuity can be accurately measured to be provided to the clinician, as well as the capacity for entering prescriptions and treatment plans for individual patients and restricting individual access to that patient's prescription and treatment plan while allowing non-occlusive operation of the system after the prescribed occlusion time or for non-patient users.
The system disclosed in US 2003/0214630 is also an occlusive device, only capable of selectively occluding the patient's amblyopic and non-amblyopic eye and it is therefore not suitable to provide binocular therapy, such as perceptual motor learning wherein two images are manipulated and spatially moved.
In WO2008/070683 a system, methods, and apparatuses for amblyopia and ocular deviation correction are disclosed. In one aspect, a system for amblyopia correction includes an image processing unit to identify a set of image parameters and, when, in operation, the image processing unit modifies a source visual content based on one or more of the set of image parameters to generate visual content and a visualization unit coupled to the image processing unit operable to receive visual content from the image processing unit, the visualization unit having a screen, when, in operation, the screen displays the visual content.
The system disclosed in WO2008/070683 works similar to standard therapy for improving binocular vision, wherein static images are employed, and therefore does not offer dynamic training. By using static images the system relies on that the patient is actively being involved in the training or exercises. The disclosed system is designed to treat amblyopia and not phoria.
Moreover, several large and cumbersome instruments are known for analyzing vision disorders, such as strabismus, amblyopia, myopia that is known as nearsightness, or accommodation disorders, Two of such devices are the VS-II Vision Screener and the Opthalmic Telebinocular, available from Keystone View, Davenport, Iowa. The Vision Screener occupies over one-half cubic foot of space, weighs more than ten pounds, and must be plugged into a wall outlet. It has a viewing head with a forehead rest and a lens system with one viewing distance of 15 inches and another of 6 meters, equivalent to optical infinity. Static targets on test slides are illuminated by reflected light. The vision screener tests for visual acuity, phorias, fusion, depth perception and color perception. Images for the left and right eye are successfully presented on a rotating target drum. However, these systems support only methods for diagnosis of eye disorders and are not adapted to provide perceptual motor training or other therapy or treatment of the diagnosed visual disorders.
Thus, there is a need for an alternative, new or improved instrument and/or method that can be used for treatment of binocular disorders such as decompensated phoria, suppression, amblyopia, and/or strabismus.
Hence, an improved patient friendly medical system, apparatus and/or method, at least suitable for treatment of binocular disorders, would be advantageous and in particular an apparatus allowing for increased flexibility, cost-effectiveness, easy handling in particular by a home user and/or user friendliness would be advantageous. There is in particular a desire to provide such a system, apparatus and/or method for providing perceptual motor learning for the visual system of a patient having binocular vision disorder, in order to establish and/or improve binocular vision of the patient. The system, apparatus and/or method are desired to have a high patient acceptance, for instance thanks to an easy to use, desirably by a sub-conscious therapy provided. Further, a convenient way of monitoring a larger patient population, without the need of costly frequent visits to eye specialists, would be advantageous.